Ethernet switches contain a table that maps Ethernet addresses to the ports of the switch via which communication with those Ethernet addresses takes place. When a packet arrives at the switch, the switch searches its table to determine via which port the packet must be transmitted.
As more and more Ethernet addresses are served by the same switch, the size of the table must grow accordingly. With Ethernet networks on the scale of a metropolitan area network, the tables of each switch become very large. As a result, the table is difficult to search, in that it requires either complex circuitry to enable it to be searched quickly, e.g., in real time, or else the chances of packets being dropped by the switch increases due to delays in searching the table. Also, such switches require large amounts of memory to store the tables, which makes the switches more costly and physically larger as well.
Furthermore, the use of such tables forces a service provider, i.e., a provider of transport via a metropolitan area Ethernet network, to deal with information relating to the network topology, e.g., the number and configuration of workstations, of the various enterprise networks for which the service provider is providing metropolitan area Ethernet service. Although not likely, this information may be abused by the service provider.